Phase-locked loops are used in integrated circuit applications, computer and processing systems, as well as in wireless and wireline communications devices. Phase-locked loops may provide a wide variety of functions, including, for example, frequency multiplication, frequency synthesis, pulse synchronization, tone decoding, and amplitude and frequency modulation and demodulation. Lower power consumption is always desirable in many of these devices, especially battery-powered devices such as portable computers and wireless communication devices, including third-generation wireless telephones that use low-power chips. In many cases, some functions on these devices, such as baseband processing functions, may go into a low-power or sleep mode to help conserve power when their function is not required. A phase-locked loop, however, is generally kept operational to allow a fast wake-up and may continue to draw power even when many other device functions are in sleep mode.
Thus there are general needs for phase-locked loops and methods of providing an output frequency.